net: dsa: move port state setters

Add a new port.c file to hold all DSA port-wide logic. This patch moves
in the code which sets a port state.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index c274130..cda218c 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -60,6 +60,11 @@ void dsa_cpu_port_ethtool_restore(struct dsa_switch *ds);
 int dsa_legacy_register(void);
 void dsa_legacy_unregister(void);
 
+/* port.c */
+int dsa_port_set_state(struct dsa_port *dp, u8 state,
+		       struct switchdev_trans *trans);
+void dsa_port_set_state_now(struct dsa_port *dp, u8 state);
+
 /* slave.c */
 extern const struct dsa_device_ops notag_netdev_ops;
 void dsa_slave_mii_bus_init(struct dsa_switch *ds);